Many life processes are regulated by the pituitary gland. This project studies how the pineal gland, influences pituitary function. The primary control of the pituitary gland is via the release of brain hormones. One of these hormones, luteinizing hormone releasing factor, regulates the release of a pituitary hormone necessary for normal reproduction, luteinizing hormone. A pineal secretion, melatonin, prevents the brain hormone from stimulating the release of luteinizing hormone. Similar effects are found using new synthetic derivatives of melatonin. The function of the pineal gland is drastically altered by environmental light and by drugs; pineal function also changes markedly during development. Thus it seems possible that as a result of these changes, and subsequent pineal-pituitary interactions, there will be significant changes in pituitary gland function resulting in turn in alterations in general health. Such an interaction may explain why the pineal gland can stop reproduction in certain animals when they are deprived of light.